The present invention relates to a rotary position transmitter for registering a rotary position of a rotary element that can rotate about an axis of rotation, where the rotary position transmitter has a sensor arrangement with at least two sensors and an evaluation circuit which is disposed downstream of the sensors and by means of which the rotary position of the rotary element relative to a reference position of the rotary element can be registered, where the sensors are capable of supplying raw signals, where, at least in the case of a slow rotary movement, power pulses are output forcibly to the sensor arrangement by a first power generation system, on the basis of which pulses it is possible to operate the sensor arrangement in each case until it is possible to determine the rotary position of the rotary element by which the rotary element has rotated in relation to the reference position when the power pulse is output, where the first power generation system and the rotary element are coupled to each other.
A rotary position transmitter of this type is disclosed by EP 0 658 745 B 1.
In the aforementioned prior art, the first power generation system is identical with the sensor arrangement. The first power generation system is always activated when the rotary element reaches a predetermined position relative to the sensor arrangement. Between these positions, no registration of the rotary position is possible. This applies even when the sensor arrangement is supplied with electrical power from outside, for example via an external power source. In addition, in the case of the aforementioned prior art, the raw signals are generated for only a short time. It is therefore possible to detect only the reaching of the predetermined position. It is not possible to register whether the rotary element then remains in this position or continues to move.
The procedure of the prior art has a number of disadvantages. The most important disadvantages consist in the fact that, firstly, only changes in the rotary position can be registered, but not rotary positions as such, and that, secondly, in the case of faster rotary movements, it is necessary to change over to a different evaluation method, since the first power generation system, which is identical with the sensor arrangement, no longer operates reliably during faster rotary movements. Furthermore, in the known prior art, either the direction of rotation can be determined only by means of a complicated evaluation of the chronological sequence of the raw signals generated when the predetermined position is reached, or a complex system is needed, on whose reliability in continuous operation limits are set.
The object of the present invention is to provide a rotary position transmitter in which reliable determination of the rotary position and of the direction of rotation of the rotary element is possible in a simple way.
The object is achieved by a rotary position transmitter which has a sensor arrangement with at least two sensors and an evaluation circuit which is disposed downstream of the sensors and by means of which a rotary position of the rotary element relative to a reference position of the rotary element can be registered,
where, in each possible rotary position of the rotary element, the sensors are capable of simultaneously supplying raw signals using which it is possible to determine by which of a number of angular ranges the rotary element has been rotated relative to the reference position,
where, at least in the case of a slow rotary movement, power pulses are output forcibly to the sensor arrangement by a first power generation system, on the basis of which pulses it is possible to operate the sensor arrangement in each case until it is possible to determine the angular range by which the rotary element has been rotated relative to the reference position when a power pulse is output,
where the first power generation system and the rotary element are coupled to each other in such a way that, by using two angular ranges which are determined solely by using the raw signals when immediately successive power pulses are output, unequivocal detection of the direction of rotation of the rotary element is possible.
The decisive advantage of the rotary position transmitter according to the invention consists in the fact that, in this regard, the sensor arrangement and the first power generation system are decoupled from each other. This is because the sensor arrangement can consequently be configured independently of the first power generation system. In particular, this means that the number of power pulses forcibly output by the first power generation system can be defined independently of the configuration of the sensor arrangement, in such a way that unequivocal detection of the direction of rotation of the rotary element is always possible.
Furthermore, because of the evaluation of the raw signals, which can be supplied simultaneously in every possible rotary position, it is always possible to determine the rotary position of the rotary element irrespective of the manner in which the sensor arrangement is supplied with power, solely by using the raw signals supplied simultaneously at one instant. This is particularly advantageous since the first power generation system outputs the forcible power pulses to the sensor arrangement with certainty only up to a limiting rotary speed. Above the limiting rotary speed, supplying the sensor arrangement with electrical power by means of the first power generation system can therefore no longer be ensured.
In order to ensure that the sensor arrangement is supplied with electrical power above this limiting rotary speed as well, the rotary position transmitter therefore generally has a second power generation system, which is coupled to the rotary element in such a way that it supplies energy continuously to the sensor arrangement, at the latest beginning at this limiting rotary speed. Beginning at the limiting rotary speed, therefore, the second power generation system undertakes the supply of power to the sensor arrangement. In addition, it is also possible for the rotary position transmitter to have supply connections, by means of which the sensor arrangement can be supplied with power from outside. In this case, changing the evaluation method during a rotary speed change, or a change to the power supply method, is not necessary.
The raw signals are preferably binary or ternary. If the raw signals are binary signals, the angular ranges are preferably equally large. If the raw signals are ternary, the angular ranges comprise basic angular ranges and intermediate angular ranges alternatingly, the basic angular ranges being larger than the intermediate angular ranges. The basic angular ranges and the intermediate angular ranges are then again equally large among themselves.
If the evaluation circuit is constructed in such a way that it checks the raw signals supplied by the sensors for plausibility and, if implausibility exists, outputs an error signal, the evaluation circuit operates particularly reliably.
If the sensors are magnetic field sensors, in particular Hall sensors, and the rotary element has a magnetic signature with at least two signature regions, the sensor arrangement needs particularly little power for operation.
The signature regions can optionally be magnetized radially or axially with respect to the axis of rotation. However, they should be equally large among themselves.
If the first power generation system and the rotary element are coupled to each other via coupling magnets, the rotary position transmitter operates particularly reliably. The coupling magnets can optionally be magnetized radially or tangentially. In this case, the coupling is particularly strong if the coupling magnets are magnetized tangentially.
The more frequently the first power generation system outputs a power pulse, the more accurately can the angular range be resolved. However, it is adequate for the first power generation system and the rotary element to be coupled to each other in such a way that the rotary element changes its rotary position by a maximum of 120xc2x0 between two immediately successive power pulses.
If the sensor arrangement can be operated in a cyclic manner in order to register and evaluate the raw signals, the result is a particularly low power requirement for the sensor arrangement. If no continuous power supply is provided, the sensors are therefore supplied with power for only a short time in each case. As a result, the energy consumption of the sensors is reduced. The sensors are thus operated in a cyclic manner at specific time intervals and in each case for a short, defined time. The important factor here is, inter alia, that the sensors are operated in a cyclic manner synchronously with each other.
If, on the other hand, a continuous power supply to the sensor arrangement is provided, the sensors are operated in continuous operation. A changeover to cyclic operation is only made if the continuous power supply fails.
It is usual for the evaluation circuit to have a revolution counter disposed downstream, by means of which a number of revolutions of the rotary element can be determined.
If the revolution counter can be supplied with power together with the sensor arrangement, the revolution counter has an electrically erasable and writable read-only memory, and the counter reading and the angular range determined during the output of the power pulses to the sensor arrangement are stored in the read-only memory during the respective power pulse, it is ensured that the current state of revolution is always known and can be registered, irrespective of the manner in which the sensor arrangement is supplied with electrical power.